Patent Document 1 teaches an outwardly-opening fuel injection valve injecting fuel in the form of a hollow cone into a combustion chamber of an engine. In the outwardly-opening fuel injection valve, an effective opening area of a nozzle port, through which the fuel is injected, varies according to the change in a lift amount of a valve body. Patent Document 2 teaches a valve covered orifice (VCO) nozzle type fuel injection valve. The VCO nozzle type fuel injection valve is configured such that a needle valve is seated directly on a seat portion where a nozzle port is open to close the nozzle port. The size of a cavity area generated on the inner peripheral surface of the nozzle port varies according to a lift amount of the needle valve. In the VCO nozzle type fuel injection valve, as well as an outwardly-opening injector, the effective opening area of the nozzle port varies according to the lift amount of the needle valve.
Patent Document 3 teaches a direct-injection engine provided with an outwardly-opening fuel injection valve disposed on the central axis of a cylinder and injecting fuel in the form of a hollow cone, wherein the fuel is injected into the cylinder in the second half of a compression stroke, thereby forming, in the combustion chamber, an air-fuel mixture layer and a gas layer around the air-fuel mixture layer. The engine disclosed in Patent Document 3 reduces cooling loss by allowing the gas layer around the air-fuel mixture layer to serve as a heat-insulating layer at the combustion of the air-fuel mixture.
Patent Document 4 teaches a compression self-ignition engine in which a wall surface defining the combustion chamber is made of a heat-insulating material to reduce cooling loss in the wall surface of the combustion chamber.